Natural draft burners are used in a variety of process apparatus, such as line heaters, reboilers, heat treaters, free water knockout drums, storage tanks and the like, commonly used in the oil and gas industry. One or more natural draft burners are supported in a firetube which extends into the vessel for transferring heat directly or indirectly thereto for heating fluids therein.
Such equipment is often located on oil and gas sites, or other industrial sites having the possibility of fugitive hydrocarbons and at which ignition sources are carefully controlled.
On-site areas having process apparatus are generally classified as Class I, Division 2, according to the National Electrical Code (NEC) or NFPA 70, a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. A similar code, the Canadian Electrical Code (CEC) or CSA C22.1, is a standard published by the Canadian Standards Association (CSA) pertaining to the installation and maintenance of electrical equipment in Canada.
An area is generally classified in North America as Class I, Division 2 when one of the following conditions exists:                volatile flammable liquids or flammable gases are handled, processed or used, but the hazardous liquids, or gases will normally be confined within closed containers or closed systems from which they can escape only in event of accidental rupture or breakdown of such containers or systems, or as a result of abnormal operation of equipment; or        ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operations of ventilating equipment; or        adjacent to a Class I, Division 1 location and to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided.        
Under the CEC, to operate a fired heater in a Division 2 area, the fired heater must be totally enclosed, all surfaces exposed to the atmosphere must operate below the temperature that would ignite a flammable substance present in the hazardous area, the combustion air intake and exhaust discharge must be equipped with a flame arresting device, and electrical components isolated from the atmosphere or at an energy level below that required to ignite a specific hazardous atmospheric mixture. Otherwise, the fired heater must be located outside the hazardous area.
A flame arrestor ensures adequacy of a flow of primary air from the surrounding atmosphere for burner combustion while preventing propagation of the flame from the burner, back along the combustion air source, to the atmosphere. The volume within a burner housing to which a flame arrestor has been installed, inherently exposed to the burner combustion conditions, is generally considered a non-classified area according to the appropriate codes.
It is common practice to utilize burner systems that are connected to burner management or control systems. Such systems both monitor burner operation, including the presence of flame, and to ensure safe start-up, operation and shutdown of the burners. The burner management system generally comprises flame-detectors for main burners and pilot burners to ensure the burners are lit. The control system is connected to fail-safe mechanisms and solenoid-operated valves for shutting off the flow of gas or vapours to the burners should a flame not be sensed. The burner control system generally comprises circuitry to re-light the burners when safe to do so and may provide communication of data to a data acquisition system. The control system also acts to modulate the burner flame intensity based on temperature requirements of the various process apparatus.
In addition to fugitive emissions in the general atmosphere about the burner system, the burner itself can be a source of combustible vapors. In the absence of a burner management system, when the flame is not present, gas could continue to flow at least to the pilot, irrespective the lack of the flame, releasing unburned fuel. Further as the process apparatus begins to demand heat, gas is also fed to the main burner irrespective of the absence of a flame. Release of gas, from the unlit pilot and main burners, to the atmosphere creates an ignition or explosion risk.
Under the various electrical codes, specific wiring requirements are established for use in hazardous or classified areas such as Class 1, Div 2. Conventional burner systems, as described above, typically utilize one or more burners and a control unit. The control unit is wired to the burners for managing the burner and for managing the valve train which supplies the gas. The control unit and connective wiring generally comprises a complex system of mechanically protected wiring systems to meet the code. “Mechanically protected” generally means that, while the electrical equipment is capable of producing sufficient energy, such as heat or electrical spark, to ignite an explosive atmosphere, it has been mechanically protected or contained so as to prevent the ignition. In the case of electrical equipment located in hazardous areas, explosion proof enclosures, rigid conduit fittings and hermetic sealing are known methods of mechanical protection. In common practice, a burner assembly, flame arrestor, burner management system or control unit and the valve train are delivered to a site. Onsite, specialized personnel are employed to electrically connect between the various components of the system, taking into consideration the necessary electrical codes, particularly where the combustion unit is to be placed in a hazardous Class 1, Division 2 area. Once connected, the system must be inspected onsite to ensure compliance with the various codes. The electrical connections are many, between various controls, valves and sensors, and each connection or junction must be in compliance.
This is a time consuming and expensive system and fraught with re-work to bring the installation into compliance. Further, if improperly installed, such systems present significant hazard to onsite personnel.
Clearly, there is a need for simplified, safe installation procedures for combustion units and cost effective wiring systems to meet the electrical code requirements.